I go through periods of being more or less sensitive. And some perfumes really set off an asthmatic reaction, although all of them are unpleasant. The expensive ones give me a worse reaction than the el-cheapo ones.
I use products with no perfumes at home, but all I have to do is take public transportation (we have no car) or sit in a restaurant chair or sit in someone's car or visit someone's home, and my clothes come home reeking of ghastly perfume. The most effective way that I have found to deal with it is to hang the clothes outside. Expensive perfumes take longer than cheap ones. Cold days (especially below freezing) breaks down the perfume faster, and really hot days (especially if there is a lot of ozone in the air) also work. Of course, ozone makes it difficult for me to breath, but I solace myself with knowing that it's at least working for me in breaking down the perfume.
If I really had MCS, like you, this would be insufficient. It is apparent that perfumes are a combination of many chemicals, only some of which are the smelly ones. I can bring the clothes inside when the smelly perfumes have broken down, but I can still smell other chemicals, which I imagine would be a problem for folks with MCS. Once I bring the clothes inside, I find that washing them in perfume-free detergent (I use Spinnrad which is available here in Germany) makes them wearable again.
I find that cigarette smoke is unpleasant and irritating (and I am SOOOO glad that new European rules have banned smoking in restaurants and public places!!!), but it doesn't affect me the way perfume does. It's just a local reaction (burning throat and eyes, unpleasant smell) rather than a whole-body reaction (asthma = difficulty breathing, throat closing up).
I rather suspect that sensitivities, including the more intense MCS, are a result of the body being unable to cope when the immune system becomes overloaded in some way. You have lived through some major health problems. The human body has some powerful mechanisms for trying to come back to health, but it can only do so much. I think that each of us has some weak link, and that's where our bodies show that they are having difficulty coping.
As you become stronger and healthier by bringing your other health problems under control, I hope that you can find more and more periods when your MCS is not so strongly reactive.